The present invention relates to a video picture generator detector of the charge transfer solid camera type operating by frame transfer. According to an envisaged application, the invention is particularly suitable for equipping a television homing apparatus, called TV homing.
In such a device, the received radiation is focused by an optical lens onto the actual detector means or sensor. The detected video signal is then processed in electronic circuits, which are a function of the intended use. The photodetector can be incorporated into a system used on the ground or into an airborne system in order to obtain an angular localization of the target, a display of the television picture or automatic tracking of the target on the basis of the angular localization or by video contrast, etc.
CTD sensors operating by frame transfer have the photodetector elements arranged in the form of an array. They are frequently constructed with CCD circuits. These sensors have a high, but stantially constant sensitivity, i.e. the variation range of the light flux trapped by the detector must remain relatively limited to obtain a satisfactory operation corresponding to a substantially linear response. Under these conditions, the detected signal has an average value corresponding to the optimum operating value provided by the manufacturer and saturation risks are eliminated.
In order to ensure automatic operation by day satisfying a solid TV camera with a CTD sensor, it is necessary to reach dynamic ranges of 10.sup.3 to 10.sup.4, the dynamic range being defined by the ratio of the maximum illumination of the scene to the minimum overall illumination. It is therefore necessary to considerably increase the light flux variation range admissible by the detector without any risk of saturation for the latter, i.e. by acting on the sensitivity to observe a video signal of substantially constant average level. It is not possible to bring about a sensitivity variation by electronic control, as is the case in practice for a conventional vidicon arrangement.
One solution which can be envisaged is the introduction of a diaphragm into the focusing optics, but the resulting rise in the dynamic range is still very limited. Moreover, for placing a TV camera with a CTD sensor within a missile homing, it is not desirable to have to provide a motorized diaphragm arrangement with respect to the optics in view of the fact that integration is made more difficult on a gyroscopic structure, a more difficult practicability and a more severe requirement imposed with regard to compactness and reliability.